In order to understand the invention, it is necessary first to consider the Regulations of the Department of Transportation as given in Tariff No. 30, entitled "Harzardous Materials Regulations of the Department of Transportation", including "Specifications for Shipping Containers".
The above regulation in Section 173.306 recognizes two types of pressure systems for metal containers.
1. For compressed gases, the container must withstand pressures of three times the pressure at 70.degree. F. PA1 2. For liquified gases, the container must withstand one and one-half times the equilibrium pressure at 130.degree. F. PA1 1. Economic advantages--lower cost. PA1 2. Safety advantages--lower pressure. PA1 3. Ecological advantages, i.e., less material is used per container, and the use of metals and plastics is conserved. PA1 4. Denting problem is solved.
In determining the pressure requirements for barrier containers, account must be taken of the fact that the initial volume in the container not filled with product is about one-third of the total volume, so that if compressed gas is used, the initial pressure is three times the final (minimum) pressure. For example, if for a given product, a minimum pressure of 33 psig is needed ( and this is also, of course, the final pressure), an initial pressure of 99 psig is required and the container must withstand a pressure of three times 99 or 297 psig. Heretofore, inert gas propellants, when used, were of this magnitude, i.e., 90-100 psig.
When a liquified propellant is used in order to maintain 33 psig at 70.degree. F., it will have a pressure of ca. 100 psig at 130.degree. F., and the container will have to withstand a bursting pressure of ca. 150 psig. To maintain an average of 66 psig at 70.degree., a pressure withstanding strength of 250 psig will be needed.
Valved pressurized containers have for the most part been designed for the discharge of atomized sprays of low viscosity fluids or for the discharge of foaming low viscosity fluids. In either case, the use of initial pressures at 70.degree. F. of ca. 35 psig for liquified gases (volatile liquids) or 100 psig for compressed gases was necessary, in order to obtain atomization or foaming. (The use of low pressure liquified gases in glass containers for the atomization of perfumes and the like required the use of high-priced propellants and valves).
When the use of barrier pressure dispensers for viscous fluids started some twenty years ago and up to the present time the only available valves and containers were small orifice valves and high pressure containers and these have been and are still in use today. The use of these containers made it necessary to warn the consumer against leaving the containers exposed to sunlight and against throwing them into incinerators or open fires because of the danger of explosion. The prior containers, therefore, had to be made of relatively rigid heavy gauge metal which increased their cost of production and transportation, and also made it difficult to eliminate denting and the by-pass or escape of the propellant.